Aeromexico and United have round-trip flights from Houston (IAH) to Mexico City (MEX) for $275-$292, NONSTOP. Flights August to November. Weekends available. Origin/Destination reversible. No Thanksgiving dates.
Some small OTAs on Skyscanner and Google have this for about $251; cheaper than the airline. If you plan on booking there, beware of any site that charges a fee to cancel a ticket within the 24-hour “free” period. Use unknown booking sites at your own risk.